Traditionally, radiation imaging technique has been widely used in container/vehicle inspection systems.
A low-energy standing wave electron linear accelerator (sometimes hereinafter referred to as accelerator) is often used as a radiation source in the radiation imaging technique. The low-energy standing wave electron linear accelerator mainly comprises a control mechanism, a modulator, a magnetron, a microwave transmission system and a ray handpiece assembly, etc.
Its working principle is that the control mechanism controls in a manner that the modulator generates high-voltage pulses, which are provided to the magnetron through a pulse transformer to thereby generate radio frequency microwaves in the magnetron. The radio frequency microwaves are fed into an accelerating tube of the ray handpiece assembly by means of the microwave transmission system to form forward waves and backward waves in the accelerating tube, which are superposed to form standing waves.
Furthermore, an electron gun power source in the modulator generates high-voltage pulses and provides the high-voltage pulses to an electron gun of the accelerating tube. By means of the high-voltage pulses, electrons are drawn out from a filament-heated cathode of the electron gun and are accelerated and transmitted to an accelerating cavity of the accelerating tube. The electrons interact with an axial standing wave electric field in the accelerating cavity and absorb energy therefrom to keep being accelerated. When the acceleration of the electrons comes to an end, the electrons are shot at a target to produce a continuous spectrum of X-rays. A shielding device and an outer collimator are used to appropriately shield X-rays oriented at other angles so as to remain an X-ray beam of a desired shape in a forward direction.
FIG. 1 is a schematic view of a microwave transmission system of a standing wave electron linear accelerator of the prior art. As shown, the microwave transmission system is connected between a magnetron and an accelerating tube to transmit microwaves generated by the magnetron to the accelerating tube, and mainly comprises a curved waveguide tube, a four-port circulator, a straight waveguide tube, a soft waveguide tube and a waveguide window.
With reference to FIG. 1, in the prior art, the microwaves from the magnetron are supplied to an accelerating tube through the microwave transmission system to accelerate electrons in the accelerating tube. Then, the accelerated electrons are shot at a target to form a continuous spectrum of X-rays. Namely, the prior art is directed to a single target standing wave electron linear accelerator.
According to the prior art described above, the standing wave electron linear accelerator can, however, only shoot a single target to produce one X-ray beam.
In regard to the container/vehicle inspection system, according to the prior art, the inspection system is a single-channel inspection system and the radiation source is a single target standing wave electron linear accelerator, so the inspection system can only transmit a continuous spectrum of X-rays to one scanning channel and is unable to conduct radiation imaging inspection for two containers/vehicles at the same time, thereby resulting in low inspection efficiency.
In regard to the mobile container/vehicle inspection system, patent document 1 (CN1490616A) discloses a mobile container inspection system. A rotatable platform is arranged on a scanning vehicle and is movable with respect to the scanning vehicle. On the rotatable platform there are a parallelogram bracket formed by four linkage bars hinged one to another and a transverse detector arm and a vertical detector arm comprising detectors and connected with the bracket. Further, a box-shaped cabin installed with a radiation source is mounted at the rear end of the rotatable platform. Upon inspection, the rotatable platform on the scanning vehicle is rotated 90 degrees, and a scanning channel is constructed from a portal-shaped frame formed of the parallelogram bracket, the transverse detector arm and the vertical detector arm. The control mechanism controls the radiation source to emit X-rays. The X-rays forming a sector pass through the container to be inspected and are received by the detectors in the transverse detector arm and the vertical detector arm so as to be converted into electrical signals and then input into an image obtaining module. The image obtaining module transmits the image signals to an image analyzing software for processing and the computer will show the detected result.
The mobile container inspection system of patent document 1 is also a one-channel inspection system and cannot conduct radiation imaging inspection for two containers at the same time, thereby resulting in low inspection efficiency.
In regard to the relocatable container inspection system, FIG. 16 shows a relocatable container inspection system disclosed in patent document 2 (CN1304038A), which comprises a mobile shielding chamber, an automatic scanning vehicle and a remote control mechanism, wherein the mobile shielding chamber is detachably assembled, and on the automatic scanning vehicle there are a portal frame consisting of a horizontal arm and a vertical arm with detectors, a radiation source and a bi-directional mobile trailer frame. According to the invention of patent document 2, since the shielding chamber can be detachably assembled and the automatic scanning vehicle can run, it is possible that the inspection system can detect at random at different places without occupying fixed inspection space and saving investment on fixed inspection location.
According to the prior art described above, the inspection system is, however, also a single-channel inspection system and is unable to conduct radiation imaging inspection for two containers at the same time, thereby resulting in low inspection efficiency.